The present invention relates generally to the field of interferometry, and, more specifically, to an interferometric system employing an optical switch configuration defining a plurality of probe arms.
In various fields of medicine and engineering it is often necessary to inspect surfaces that are difficult to reach. For example engine cylinders, compressors for jet aircraft engines, heat exchangers, internal organs, cavities, and arterial passageways in a patient. Biomedical imaging technology, for example, magnetic resonance imaging, X-ray computed tomography, ultrasound, and confocal microscopy could be used to inspect and characterize a variety of tissues and organs. However, there are many situations where existing biomedical diagnostics are not adequate. This is particularly true where high resolution, about 1 micron, imaging is required. Resolution at this level often requires biopsy and histopathologic examination. While such examinations are among the most powerful medical diagnostic techniques, they are invasive and can be time consuming and costly. Furthermore, in many situations conventional excisional biopsy is not possible. Coronary artery disease, a leading cause of morbidity and mortality, is one important example of a disease where conventional diagnostic excisional biopsy cannot be performed. There are many other examples where biopsy cannot be performed or conventional imaging techniques lack the sensitivity and resolution for definitive diagnosis.
A borescope is an optical device such as a prism or optical fiber that can be used to inspect inaccessible spaces. An endoscope is an instrument for visualizing the interior of a hollow organ like a colon or esophagus. The observed part of the internal surface is illuminated by an illumination channel and the optical observation system allows investigation of the internal space surface. During inspection it is often advantageous and important to investigate lateral surface in the space.
Elements allowing a change in the direction of optical observation permits inspection inside spaces and lateral surfaces that a rigid borescope or endoscope cannot view. Endoscopes and borescopes have included a means of articulating the tip of the scope so that it bends in several directions to look around a cavity. However, in many applications, for example arteries, there is insufficient room in the cavity or conduit for articulation of the scope tip.
Rather than being flexible, a rigid endoscope contains a mount, an optical system for observation, and a light guide. The mount and the light guide are placed in a tube housing. The optical axes of the observation and illumination system for lateral direction are deflected at an angle with respect to the lens optical axis with the help of a prism. In order to observe the entire lateral surface along the whole transverse perimeter of the investigated cavity, it is necessary to rotate the entire endoscope housing around the axis of symmetry. Fiber optic inspection devices contain a lens in a mount and illumination lamps installed in a housing at a lateral wall of the housing where a window is provided. Lateral observation is performed by way of a reflection prism situated opposite the window. For panoramic observation of the walls in a space the entire housing needs to be rotated. In some instruments the illumination source must also be rotated complicating the design and operation of such a device.
Current methods for screening and diagnosis of pathologic conditions in tissue such as cancer often involve surgical biopsy of the tissue followed by histological evaluation. This procedure is not only invasive, time-consuming and expensive but often is not capable of rapid and reliable screening of a large surface such as the colon, esophagus, or stomach. Since early diagnosis and treatment tend to be critical to effective and successful treatment of these pathologies, the development of better techniques and devices for diagnosis and screening would result in improved clinical outcomes.
Optical coherence tomography (OCT) is an imaging technique, which allows high-resolution observation and characterization of tissue microstructure imaging with resolution on the order of microns. This technique measures detailed changes within a few millimeters of a non-transparent tissue structure. One drawback of the OCT imaging is the time required to obtain images over a sufficient area.
Optical coherence domain reflectometry (“OCDR”) is an optical technique that uses a scanning Michelson interferometer in conjunction with a broadband illuminating source and cross-correlation detection.
Both OCDR and OCT use optical data collected by a single mode optical fiber to determine the morphology, physical properties and location of various types of interspersed materials or biological tissue. Typically a probe used in conjunction with either OCDR and OCT includes an optical fiber having a head at its distal tip. Alternatively, inserting an optical fiber concentrically into a thin-wall flexible hypodermic stainless-steel tube and fastening it with cement form the probe. A window in the tube allows light to pass to and from the head at the tip of the optical fiber. The probe is then inserted into the tissue or organ to be examined. Light emitted by the head of the optical fiber is reflected from the adjacent body of tissue or organ. The head then collects the reflected light, also known as “back-scattered” light.
Using a Michelson interferometer in conjunction with this apparatus the morphology, properties, and location of the various materials, tissue, or organ elements that caused the back-scattered light are determined and an image generated to provide a real-time visual display of the device, body of tissue, or organ being examined.
However, as a typical optical fiber can only emit light and gather back-scattered light along its axial centerline, it is limited to viewing straight ahead. A view transverse to the axial centerline of the fiber has been obtained by turning or bending the head of the fiber perpendicular to its axial centerline, and this is often very difficult or even impossible in the close confines typically encountered during surgical procedures, or in examining the sides of an artery or vein.
Mounting a gradient refractive index lens or a mirrored corner cube on the head of the optical fiber has been used to obtain lateral scans. Either a gradient refractive index (GRIN) lens or a mirrored corner cube deflect the emitted light at an angle transverse to the axial centerline of the optical fiber, and thus provide for lateral viewing. However, these apparatus add bulk to the head of the optical fiber. For example, the diameter of an optical fiber typically used in conjunction with OCDR and OCT is on the order of about 90 microns, while the diameter of the smallest GRIN lens is about 150 microns and that of the smallest mirrored corner cube is about 125 microns. The use of either of the aforementioned optical devices thus renders some locations inaccessible and makes the optical fiber more difficult to maneuver. In addition, extremely small GRIN lenses and mirrored corner cubes are quite expensive, and very fragile. Their use thus adds to the cost of the probe, and renders it prone to malfunction.